OXIDIZING EFFECT ON METAL REMOBILIZATION AND DAPHNIA SIMILIS TOXICITY FROM A BRAZILIAN RESERVOIR SEDIMENT SUSPENSION

Anoxic sediment suspension assays were performed on Billings Reservoir (SP-Brazil) samples. The effect of oxidation on metal remobilization compared to control suspensions maintained in reducing conditions was evaluated. Suspension samples from the oxidizing and reducing system were sampled during a 15-day period. Samples were centrifuged and filtered, and the water phase obtained was used in Daphnia similis 48 h toxicity tests and metals analysis. The reducing system (Eh < −65 mV, pH 6.5) indicated high Fe and Mn values in water with toxicity ranging from 3 to 11.8 toxic units. In contrast, in the oxidizing system (Eh 500 mV, pH < 3.0), Zn, Cd, Cr, Ni and Pb were mobilized on days 7–15, corresponding to a drastic increase in toxicity (357 toxic units). These data indicate that laboratory oxygenation of highly acid productive field-collected sediments causes increased metal mobilization and toxicity, suggesting that similar responses may occur in the field after dredging activities or natural resuspension of sediments. © 1998 Elsevier Science Ltd. All rights reserved